06-24-2008, 06:16 AM
I have been using TYVEK for many years. I would not suggest using it between layers of siding or over solid shear. There seems to be some problems with capillary movement of vapor that becomes liquified between the TYVEK and the shear, or in your case, the T-111. I have been told that TYVEK no longer meets code in California. Code now calls for 15# felt. 15# felt would be my suggestion.
Dan